Elastomerically mounted chain saw



United States Patent Inventor Otto H. Scharpl Brookfield, WisconsinAppl. No. 698,781 Filed Jan. 18, 1968 Patented Sept. 29, 1970 AssigneeOutboard Marine Corporation Waukegan, Illinois a corporation of DelawareELASTOMERICALLY MOUNTED CHAIN SAW 16 Claims, 6 Drawing Figs.

US. Cl 143/32, l73/l62,92/l61 Int. Cl B27b 17/00 Field of Search 143/32;

[56] References Cited UNITED STATES PATENTS 3,224,473 12/1965 Dobbertinet al 143/32 3,372,718 3/1968 lrgens 143/32 Primary Examiner-Donald R.Schran Attorneys-Wheeler, Wheeler, House and Clemency and Robert K.Gerling ABSTRACT: Disclosed herein is a chain saw in which the upper andrear handles, the gas tank and the cutter bar are rigidly secured to aframe to form a frame assembly. The engine is mounted relative to theframe assembly so that the crankshaft is parallel to the cutter bar andthe piston reciprocates about a generally vertical axis when the saw isin an upright horizontal position. A sprocket shaft for driving acutting chain is rotatably supported by a portion of the engine block atright angles to the crankshaft. The engine is mounted to the frameassembly by clastomeric engine mounts which have a low spring rate inthe direction of shear and a high rate in the direction ofcompression.

Patented Sept'ZQ; 1970 Sheet 2 of 2 ELASTOMERICALLY MOUNTED CHAIN SAWBACKGROUND OF INVENTION It is known to isolate a chain saw engine fromthe handles by rubber mounts. In mounting arrangements of this natureand in particular where the cutter bar is connected directly to theengine block, the mounts must be made soft to provide effectiveisolation because of the low mass of the handles relative to the engineand saw bar. As a result, any loading or prying action applied on thesaw bar during the cutting operation, as for instance, to remove apinched bar, must pass through the soft mounts, resulting in loss ofcontrol and loss of prying force.

SUMMARY OF INVENTION The invention provides a chain saw comprising anengine which is resiliently mounted on a frame, a shaft carrying asprocket which is supported independently of the frame by bearings onthe engine, a cutter bar mounted from the frame, and a saw chain trainedaround the sprocket and the cutter bar. More particularly, the inventionprovides a chain saw in which the cutter bar handles and gas tank aresecured to a frame to form an integrated frame assembly. Relative motionbetween the sprocket and the frame assembly is minimized by an enginemounting arrangement wherein the engine piston travels in a verticalplane and at right angles to the direction of chain pull when the chainsaw is in an upright horizontal position. More specifically, the planeof the shaking force incident to engine operation is vertical and atright angles to the chain pull, when the saw is in an upright positionwith the piston reciprocating in a vertical direction and the directionof chain pull is horizontal. The alignment of the engine in this manneris afforded by the use of a right angle drive connecting the enginecrankshaft which is parallel to the cutter bar to a sprocket shaft whichis at right angles to the cutter bar, and which is rotatably supportedby a portion of the engine block.

Such arrangement permits the use of engine mounts connecting the engineto the frame assembly which have a low rate in the direction of shearwhich is also parallel to the plane of the shaking force. The use ofsoft mounts effectively isolates engine vibration from the handles andcutter bar.

The engine mounts have a relatively high rate in the direction ofcompression to minimize, during cutting, any sprocket shaft displacementwhich could cause misalignment or slack in the chain between thesprocket and cutter bar.

Vibration in the forward engine mounts and vibration in the frameassembly is further minimized by locating the shaking force of theengine and distributing the mass of the engine so that the shaking forceof the engine is at the approximate center of percussion of the enginemass with respect to the forward engine mounts. Because of the proximityof the forward mounts to the sprocket axis and as a consequence of theyieldability of the forward mounts in the direction of shear and inresponse to engine vibration, during operation, the engine tends topivot about the sprocket axis rather than to transfer vibration orimpulses to the frame assembly.

In addition. the center of gravity of the engine is located forwardly ofthe plane of the shaking force to minimize the amplitude of the enginevibrations in the forward mounts and sprocket shaft.

Rear engine mounts are provided between the engine and frame assembly onopposite sides of the piston and near the plane of the shaking force,i.e., a plane at right angles to the crankshaft through the center lineof the piston and the cylinder. The rear mounts have a low rate in shearto afford pivotal movement ofthe engine about the forward mounts.

Because the chain saw bar is part of the rigid frame assembly ratherthan being secured to the engine, control of the cutter bar is not lostduring prying action or movement to remove a pinched bar.

Further objects and advantages of the invention will become apparentfrom the following description and accompanying drawings.

DRAWINGS FIG. 1 is a side elevational view of a chain saw in accordancewith the invention.

FIG. 2 is a rear or end view, in fragmentary section, of the chain sawshown in FIG. 1.

FIG. 3 is a plan view, in fragmentary section, of the chain saw shown inFIG. 1.

FIG. 4 is a diagrammatic plan view of the chain saw disclosed in FIG. 1.

FIG. 5 is a diagrammatic perspective view of the chain saw disclosed inFIG. 1.

FIG. 6 is an alternate construction for the forward mount between theengine and frame.

DETAILED DESCRIPTION The invention relates to a chain saw in which thefront and rear handles, the cutter bar and gas tank are secured to aframe to form an integrated frame assembly. The mass distribution of theengine and the location of the engine mounts are arranged relative tothe frame assembly to obtain maximum vibration isolation of the enginefrom the frame assembly. I

More specifically and referring to the drawings, a chain saw 10embodying the invention is provided with a frame assembly 11 whichincludes a frame 12 (see FIGS. 4 and 5). The frame 12 includes aU-shaped portion 14 having side legs 16 and 18. The frame 12 alsoincludes a rear handle portion 20, upper handle portion 21 and a lowerframe portion 22. A gas tank 24 is connected to the forward end of theside legs 16 and 18 to form a forward portion of the frame assembly 11.

Referring to FIG. 1, a cutting chain 26 is supported by a cutter bar 28(see FIG. 5) which is generally parallel to the side legs 16 and 18 ofthe frame 12. The cutter bar 28 is bolted or otherwise rigidly securedto the frame 12 by bolts 30 and forms an integral part of the frameassembly 11.

The cutting chain 26 is driven (see FIG. 2) by an engine 32 having anengine block 33 and a piston 34 which reciprocates about a generallyvertical axis when the chain saw is in the upright position of FIGS. Iand 2. The piston 34 is connected to the crank 37 of a crankshaft 36which is generally parallel to the frame side legs 16 and 18 and thecutter bar 28 and which extends fore and aft of the chain saw 10 and isin a horizontal position when the chain saw is in its upright positionillustrated in FIGS. 1 and 2.

Power is supplied to the chain 26 (see FIG. 3) by a sprocket 38 locatedat one end of a sprocket shaft 40 which is rotatably supported free ofthe frame assembly 11 by bearings 42 mounted in a portion of the engineblock 33 for rotation about an axis perpendicular to the crankshaft 36and the cutter bar 28. Means are provided for drivingly connecting thesprocket shaft 40 to the crankshaft 36. In the disclosed construction,the means comprises a bevel gear .43 at one end of the crankshaft whichmeshes with a bevel gear 44 on the sprocket shaft. Thus, the engineblock and right angle drive is a unitary structure and is supported bythe frame assembly 11 as hereinafter described. The use of a right angledrive with the piston 34 reciprocating in a vertical plane when thechain saw 10 is in the upright position shown in FIGS. 1 and 2 permitsthe use of mounts which have a low rate in the plane of engine vibrationas hereinafter described in detail.

In accordance with the invention, the mass of the engine 32 isdistributed so that the shaking force incident to engine operation,i.e., the force caused by reciprocating movement of the piston 34 andthe rotary motion of the crank 37, is located at the center ofpercussion of the engine mass in relation to the forward mounts of theengine to thus minimize vibration in the frame assembly 11 and therebyalso to minimize vibration i the forward engine mounts.

It is well known that if a blow strikesa pivoted or pendulum suspendedbody or the body receives an impulse at a certain point spaced from thepivotal axis, the impulse will cause only pivotal movement of the bodyabout the pivotal axis rather than translatory motion or vibration ofthe entire body. The point at which the impulse or blow must strike thebody to cause only pivotal movement ofthe body about its pivotal axiswith no impulse being received at the pivotal axis is called the centerof percussion. The location of the center of percussion relative to thepivotal axis can be determined by the equation or law of physics L=llmlwherein L=the distance of the center of percussion from the pivotal axis0, I the moment of inertia of the body about the pivotal axis 0, mi themass ofthe body and I the distance between the center of mass of thebody and the pivotal axis 0. The derivation of this equation can befound in the text Principles of Physics" by Sears, Vol. I, pp. 275, 276,published in 1947 by Addison, Wesley Press, Inc. Additional backgroundof the principles involved is set forth in the text Mechanics" by Lymon,published in 1953 by Addison-Wesley Publishing Company, Inc.

The location of the plane of the shaking force of the engine 32 at orapproximately at the center of percusion of the engine mass and at adistance L from the pivotal axis of the engine mass, i.e., the forwardengine mount, to prevent or minimize vibrations or impulses from beingreceived at the forward engine mount, can be determined mathematicallyby the above law of physics or can be determined empirically. The centerof mass 45 of the engine can be varied by moving the flywheel 46 fore oraft on the crankshaft 36.

The distribution of the engine mass so that the center of gravity isforward of the shaking force reduces the amplitude of the enginevibrations in the sprocket shaft and forward mounts.

in accordance with the invention, means are provided for pivotallymounting the engine to the frame to afford a pivotal axis foroscillatory movement of the engine 32 in response to shaking forcesincident to engine operation.

in the construction disclosed in FIGS. 3, 4 and 5 the means comprisestwo forward mounts 50 composed ofan elastomeric substance such asrubber. The mounts 50 are located between and secured to the forwardpart 51 of the engine block 33 and the gas tank 24. Threaded studs (notshown) extending from the mounts can be employed to secure the mounts50in place. The mounts have a relatively low rate in shear, i.e., aresoft in a vertical direction, to yieldably afford a pivotal axistransverse to the cutter bar for osicllatory or pivotal movement of theengine. The forward mounts 50 desirably have a high rate in thedirection of compression, which direction is also the direction of chainpull so as to avoid misalignment of the sprocket 38 and the chain sawbar 28 due to chain pull during the cutting operation, but at the sametime, yieldably afford limited translatory movement of the engine in thedirection of chain pull. A typical mount 50 can have a shear rate orlateral spring rate such that a 240 pound force will deflect the mountsl inch, and a compression rate of five times that value or 1,200 poundsper inch. A single forward mount can be employed between the forwardpart of the engine block 33 and the gas tank 24 to obtain some of theadvantages of the invention.

An alternate construction for the forward mounts is shown in FIG. 6. inthis construction, the forward mount comprises an elastomeric hinge 56which has an elongate portion of elastomeric material 58 sandwichedbetween two plates 60 and 62. The elastomeric material is bonded to theinner surface ofthe plates 60 and 62. The plate 60 is bolted to the gastank and the plate 62 is bolted to the engine. The hinge 56 has arelatively high rate of deflection in compression in the direction ofthe cutter bar and is yieldable in the direction of shear, i.e., in avertical direction when the engine is located as shown in HQ It iswithin the purview of the invention to utilize either the forward mounts50 or the sprocket axis as the pivotal axis of the engine mass, with theplane of the shaking force located at a distance L from either theforward mounts 50 or at a distance L from the sprocket axis.

The invention also includes means for yieldably mounting the engine atthe plane of the shaking force to the frame assembly 11. The meanscomprises two rear elastomeric mounts 66 which have a low rate in thedirection of shear, i.e., a vertical plane when the chain saw 10 is inan upright position as shown in FIG. 1, to afford vibration isolationfrom the frame and a high rate in compression which is the horizontaldirection of the chain pull when the chain saw is in this position. Themounts 66 can have a shear rate equal to the forward mounts so that a240 pound force will deflect the mounts 1 inch.

The mounts 66 are located between depending frame members or brackets 68and the engine block. The mounts 66 may be secured in this position bybolts 70, which, as shown in FIG. 3, extend through the dependingbracket 68 and mounting lugs 72 on the block. To provide balance andstability of the engine block relative to the frame, the mounts arealigned so that a plane connecting the centers of the rear mounts 66will intersect the center of gravity or center of mass 45 of the engineblock.

in operation of the chain saw 10 of the invention, the forward mounts 50readily yield in shear to isolate engine vibrations from the frameassembly 11.

Various 0f the features of the invention are set forth in the followingclaims.

I claim:

1. A chain saw comprising a frame, an engine having reciprocating partsproviding a shaking force incident to engine operation, a cutter barmounted on said frame independently of said engine, a sprocket shaftsupported by said engine independently of said frame, a chain sprocketon said shaft, a cutting chain trained around said sprocket and aroundsaid cutter bar, and means for pivotally mounting said engine to saidframe at a location spaced from the center of engine mass remote fromsaid reciprocating parts whereby said engine is oscillatable about saidpivotal mounting means in response to shaking forces.

2. A chain saw in accordance with claim 1 wherein said engine isarranged with respect to said means pivotally mounting said engine sothat the distance L from the plane of the shaking force to the pivotalaxis of said engine mounting means is governed by the law of physics LI/ml where l is the moment of inertia of the engine about the pivotalaxis, m is the mass of the body and I is the distance between the centerof mass ofthe engine and the pivotal axis.

3. A chain saw in accordance with claim 1 wherein said means pivotallymounting said engine to said frame comprises an elastomeric mount whichhas a low rate in the direction of shear and comparatively high rate inthe direction ofcompression.

4. A chain saw in accordance with claim 1 wherein said means pivotallymounting said engine comprises a hinge hav ing an inner layer ofelastomeric material sandwiched between two mounting plates, one of saidmounting plates being secured to said engine and the other of saidmounting plates being secured to said frame.

5. A chain saw in accordance with claim 1 including means for yieldablymounting the engine to said frame adjacent to the plane ofthe shakingforce.

6. A chain saw in accordance with claim 5 wherein said engine hasmounting lugs located adjacent to the plane of the shaking force andsaid frame has brackets, and elastomeric mounts interposed between saidlugs and said brackets.

7. The device of claim 6 wherein a plane connecting the centers of saidmounts intersects the center of mass of said engine.

8. A chain saw comprising a frame, a cutting chain, a cutter bar forsupporting said cutting chain, said cutting bar being secured to saidframe, an engine having a piston which reciprocatcs at right angles tothe direction of pull of said cutting chain during cutting action, saidengine having a crankshaft extending parallel to said cutter bar, asprocket shaft at right angles to said crankshaft, means on said enginefor rotatably supporting said sprocket shaft, means for drivinglyconnecting said crankshaft to said sprocket shaft, and means formounting a part of said engine to said frame, said means for mounting apart of said engine to said frame being yieldable in a directionparallel to the direction of travel of said piston, and said lastmentioned means being less yieldable in the direction of chain pull thanin the direction of travel of the piston.

9. The device of claim 8 wherein said means for mounting a part of saidengine to said frame comprises an elastomeric mount located between theforward part of said engine and said frame, said mount having acompression rate greater than the shear rate.

10. The chain saw of claim 8 including means for yieldably mounting saidengine to said frame, said means being located between said engine andsaid frame adjacent the piston,

11. The chain saw of claim 8 wherein said means for rotatably supportingsaid sprocket shaft comprises bearings supported by a portion of saidengine.

12. A chain saw comprising a frame assembly including a frame having aU-shaped portion with side legs, a front handle connected to said frame,a rear handle connected to said frame, a gas tank secured to the forwardend of said side legs, a cutter bar secured to said frame, a cuttingchain movably supported by said cutter bar, with the direction of chainpull during operation being at right angles to the plane ofreciprocation of said piston, a sprocket shaft, an engine rotatablysupporting said sprocket shaft and having a piston which reciprocates ina plane perpendicular to said sprocket shaft, and means for mounting apart of said engine to said frame assembly, said means being readilyyieldable in a direction parallel to the plane of reciprocation of saidpiston and less yieldable in the direction of chain pull as compared tothe direction parallel to the plane of piston reciprocation.

13. A chain saw in accordance with claim 12 wherein said means formounting a part of said engine to said frame assembly compriseselastomeric mounts located between the forward portion of said engineand said gas tank and including means for yieldably mounting said engineto said frame assembly, said means being located adjacent said pistonand between said engine and said frame. I

14. A chain saw comprising a frame, a cutting chain, a cutter barsupporting said cutting chain, said cutter bar being secured to saidframe, an engine having a piston which reciprocates at right angles tothe direction of pull of said cutting chain during cutting action, asprocket shaft supported by said engine independently of said frame, asprocket on said shaft and around which said chain is trained, andresilient means for mounting said engine from said frame, said enginemounting means being located such that the center of mass of said engineis located intermediate said piston and said engine mounting means.

15. A saw chain in accordance with claim 14 wherein said engine mountingmeans is yieldable in the direction parallel to the direction of travelof said piston and wherein said engine mounting means is less yieldablein the direction of chain pull as compared to the direction parallel tothe direction of piston travel.

16. A chain saw comprising a frame, an engine, means resilientlymounting said engine on said frame, a cutter bar mounted on said frame,a sprocket shaft supported independently of said frame by bearings onsaid engine, a sprocket on said shaft, and a saw chain trained aroundsaid sprocket and said bar.

